Electrode material for electrochemical element and method for production thereof, and electrochemical element

[0001] Technical Field The present invention relates to an electro of using the electrode for an electrochemical device material manufacturing method thereof and the electrode material relates optical element, more specifically, conductive material particles and composite of a metal oxide The present invention relates to an electrode material made of the same material, a method for producing the same, and an electrochemical element such as a lithium secondary battery or an electrochemical capacitor using the electrode material.

(Background Technology) Lithium secondary battery electrodes, especially positive electrodes, are LiCoO.₂A positive electrode active material made of a metal oxide such as carbon and a powder of a conductive substance such as carbon are mixed with an organic solvent solution or an aqueous dispersion of a binder to prepare a positive electrode mixture-containing paste, and a positive electrode mixture-containing paste is prepared. It is produced through a step of forming a thin-film positive electrode mixture layer on the current collector by applying it to a current collector made of a metal foil or the like and drying it.

[0003] However, although the lithium secondary battery having the positive electrode produced as described above has a high energy density, since the positive electrode active material is originally an insulator, it is charged under a high current density (under a high load). It is not possible to sufficiently cope with discharge, and high capacity cannot be obtained. In addition, a binder is always required to retain the active material and maintain the shape of the positive electrode, and therefore, the binder, which is an insulator, inhibits the conductivity and further deteriorates the characteristics under a high current density.

[0004] In addition, research has been conducted on electrochemical capacitors that utilize the redox reaction of lithium, and efforts are being made to increase the output by making the active material finer and by mixing a large amount of conductive material. If this is done, the bulkiness will increase and the bulkiness density will decrease, and since the conductive substance is also generally bulky, the filling property of the electrodes will deteriorate and a high energy density cannot be obtained. Further, if the filling property is poor, a gap is formed between the active substance and the conductive substance, and the contact property is not always good, so that sufficient conductivity cannot be ensured.

(Disclosure of the Invention) An object of the present invention is to solve the above-mentioned problems of the conventional electrode material for an electrochemical element, to show a high capacity even under a high current density, to have an excellent filling property, and to lithium. An object of the present invention is to provide an electrode material suitable for use in an electrochemical element such as a secondary battery or an electrochemical capacitor, and an electrochemical element using the electrode material.

[0006] As a result of conducting various studies to achieve the above object, the present inventors have conducted various studies, and as a result, oxides of metal elements belonging to the range of Group 3 to Group 12 in the 4th to 6th periods of the periodic table. By adding conductive substance particles to the colloidal solution of the above, mixing and dispersing, and heat-treating this, it is composed of a composite of the conductive substance particles and the oxide of the metal element, and has a high capacity even under a high current density. We have found that an electrode material having a high bulk density and excellent filling property can be obtained, and have completed the present invention.

[0007] According to the first gist of the present invention, colloidal liquids and conductive substance particles of oxides of metal elements belonging to the range of Group 3 to Group 12 in the 4th to 6th periods of the timetable.<u style="single">Carbon powder</u>Obtained through heat treatment of the mixed dispersion with<u style="single">, Has lithium ion doping / dedoping function,</u>An electrode material for an electrochemical element, which is composed of a composite of a metal oxide and conductive substance particles, is provided.

[0008] According to the second gist of the present invention, the conductive substance particles and the oxides of metal elements belonging to the range of Group 3 to Group 12 in the 4th to 6th periods of the periodic table.<u style="single">Weight ratio from 30:70 to 90:10</u>It is a composite, and an oxide film of the metal element is formed on the surface of the conductive substance particles with a thickness of 0.5 to 10 nm.<u style="single">, Has a lithium ion doping / dedoping function</u>An electrode material for an electrochemical device is provided.

[0009] The electrode material for an electrochemical element of the present invention has a high bulk density, excellent filling property, and high filling as compared with a material obtained by simply mixing a metal oxide and a conductive substance in a dry manner. In addition, since the surface of the conductive substance particles is coated with the metal oxide, the contact property between the conductive substance and the metal oxide is improved and the conductivity is improved, and a high capacity is provided even under a high current density. The electrochemical element shown can be configured.

[0010] In the present invention, the metal oxide used in the production of the electrode material is an oxide of a metal element belonging to the range of groups 3 to 12 in the 4th to 6th periods of the periodic table. Specific examples of oxides of metal elements belonging to the range of Group 3 to Group 12 in the 4th to 6th periods of the periodic table include, for example, Sc, Ti, V, Cr, Mn, Fe, and Co. , Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Pd, Ag, Cd, lanthanoids, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg and other oxides. In particular, oxides of metal elements belonging to the range of groups 5 to 10 of the 4th period of the periodic table such as V, Cr, Mn, Fe, Co, Ni, and those metal elements and other metal elements A composite oxide containing at least one of them is preferable. Further, the oxide of the metal element may contain an element other than the element, for example, Si, Sn, Al, an alkali metal element or an alkaline earth metal element, that is, Li or Mg. It may be contained.

[0011] As the conductive substance particles, for example, carbons such as acetylene black, carbon black, activated carbon, carbon fibers and carbon nanotubes, and metal powders such as aluminum, titanium and nickel can be used. The conductive substance particles may be primary particles or secondary particles, and may be a chain of particles such as acetylene black. The mixing ratio (weight) of the metal oxide and the conductive substance is preferably 70:30 to 10:90, particularly preferably 50:50 to 25:75. The oxide of the metal element is made into a colloidal liquid and then mixed with the conductive substance particles.

[0012] In the preparation of a colloidal solution of a metal oxide, it is usually difficult to directly convert the metal oxide itself into a colloidal solution. Therefore, the metal powder is mixed with a solution containing an oxidizing agent such as hydrogen peroxide, or It is preferable to prepare by mixing a metal acetate, nitrate, carbonate or the like with a liquid containing an oxidizing substance. For the mixing and dispersion of the colloidal liquid of the oxide of the metal element and the conductive substance particles, any mixing means such as stirrer, ball mill, and ultrasonic dispersion can be adopted, and the temperature and time at the time of mixing thereof. The above is not particularly limited, but for example, it is preferable to mix and disperse at 0 to 40 ° C. for about 1 to 12 hours. The heat treatment after the mixing and dispersion may be carried out after the mixture of the metal oxide and the conductive substance is separated from the dispersion to some extent by filtration, centrifugation or the like, or the mixed dispersion may be used as it is. May be good.

[0013] The conditions during the heat treatment are not particularly limited, but the temperature is preferably 50 ° C or higher, more preferably 80 ° C or higher, and more preferably 450 ° C or lower, preferably 300 ° C or lower. Is more preferable. The time is preferably 1 hour or more, more preferably 3 hours or more, preferably 24 hours or less, and more preferably 10 hours or less. In particular, when carbons are used as the conductive substance particles, a carbon oxidative decomposition reaction occurs when the temperature exceeds 450 ° C. Therefore, it is preferable to perform the heat treatment at a lower temperature than when using metal powder, and the temperature is 300 ° C. It is more preferable to perform the heat treatment at C or lower.

[0014] When the electrode material composed of the composite of the metal oxide and the conductive substance obtained through the above heat treatment is observed with a transmission electron microscope, the presence of black contours is observed on the surface of the conductive substance particles. , The energy dispersive X-ray microanalyzer confirms that the black outline is a metal oxide. That is, it is confirmed that the electrode material of the present invention has the above-mentioned metal oxide film formed on the particle surface of the conductive substance. The thickness of the coating film is preferably in the range of 0.5 to 10 nm. This is because a thickness of 0.5 nm or more provides a sufficient capacity as an electrode material, and a thickness of 10 nm or less improves conductivity and provides sufficient output characteristics.

[0015] Further, in the present invention, the electrode material is "an oxide of a metal element belonging to the range of groups 3 to 12 in the 4th to 6th cycles of the periodic table and conductive substance particles. Although it is expressed as "composite", this does not mean that the electrode material is composed only of the metal oxide and the conductive substance, but is a part of the metal oxide or the conductive substance. May be changed to another substance by the above heat treatment, and may contain other substances within a range that does not adversely affect its properties. It can be expected to improve cycle characteristics.

[0016] The electrode material produced as described above has a lower bulk than a mixed powder obtained by simply mixing a metal oxide and a conductive substance, and when expressed in terms of bulk density, the bulk is bulky. It has a high density and excellent filling property as an electrode material. That is, the bulk density is the density including the space existing between the individual powders when the powder is filled in the container, and is obtained by dividing the weight that can be filled in a predetermined volume by the value of the volume. The higher the bulk density value, the lower the bulk of the powder and the better the filling property. However, since the suitable value of this bulk density differs depending on the metal oxide or the conductive substance, it cannot be unequivocally determined which range is preferable. However, according to the present invention, the bulk density of the electrode material can be determined. , It can be increased to about 15-60% of its true density.

[0017] In order to prepare an electrode using the obtained electrode material, a binder such as polytetrafluoroethylene or polyvinylidene fluoride is added to the electrode material and mixed, and the obtained electrode mixture is mixed by an appropriate means. It may be molded. For example, the electrode mixture is pressure-molded, or the electrode mixture is dispersed in a solvent to prepare an electrode mixture-containing paste (in this case, the binder is dissolved in the solvent in advance and then the electrode material is used. It may be mixed), and the obtained electrode mixture-containing paste is applied to a current collector made of a metal foil, a metal net, etc., and dried to form a thin electrode mixture layer. Will be done. However, the method for producing the electrode is not limited to the above-exemplified method, and other methods may be used. For example, the same current collector is immersed in a mixed dispersion of a colloidal solution of a metal oxide and a conductive substance, or the mixed dispersion is applied to a current collector and mixed and dispersed in the current collector. The electrode may be prepared by heat-treating after adhering the liquid. In this case, an appropriate amount of an aqueous dispersion of a binder such as polytetrafluoroethylene can be added to the mixed dispersion of the colloidal solution of the metal oxide and the conductive substance, but the electrode material of the present invention is a current collector. Since it has a sufficient binding force with and, the electrode can be manufactured without containing a binder. Therefore, it is possible to provide an electrochemical element having extremely good output characteristics.

Since the electrode material of the present invention has a lithium ion doping / dedoping function, it can be used as an electrode material for an electrochemical element such as a lithium secondary battery or an electrochemical capacitor. Also<u style="single">,Book</u>Since the electrode material of the present invention exhibits high capacity even under high current density, lithium secondary power is a driving power source for applications requiring high output, such as electric vehicles and electric bicycles.<u style="single">Pond or</u>Suitable as an electrode material for electrochemical capacitors and the like.

[0019] The electrode material of the present invention has a high bulk density and is excellent in filling property as compared with a conventional electrode material composed of a mixed powder of a metal oxide and a conductive substance, and an electrode can be produced without a binder. it can. Further, by using this electrode material, it is possible to provide an electrochemical element that exhibits a high capacity even under a high current density.

Examples Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

[0021] Example 1 1 g of metallic vanadium and 100 ml of 30 mass% hydrogen peroxide solution were mixed, and the mixture was stirred and mixed in an ice bath for 3 hours. Leave this for 24 hours to vanadium pentoxide (V)₂O₅) Was solified to obtain a colloidal solution. To 5 g of the obtained colloidal solution of vanadium pentoxide, 0.1 g of acetylene black, 2 g of water and 1 g of acetone were added, and the mixture was mixed and dispersed by stirring with a stirrer for 3 hours, and then heat-treated at 120 ° C. for 3 hours to produce vanadium pentoxide. And acetylene black were obtained. The ratio of vanadium pentoxide to acetylene black in this complex is 7:10 by weight, and the true density of this complex is 2.4 g / cm.³Met.

[0022] When 5 g of this complex was filled in a graduated cylinder and vibration was applied until there was no volume change to measure the bulk density, the bulk density of this complex was 0.50 g / cm.³It was a value of 21% of the true density. As a result of analyzing this complex with a transmission electron microscope and an energy dispersive X-ray microanalyzer, it was confirmed that a vanadium pentoxide film 2 having a thickness of about 5 nm was present on the entire surface of the carbon particles 1. FIG. 1 shows a schematic view showing the shape of the complex of Example 1, and FIG. 2 shows a schematic view showing the cross-sectional shape thereof.

Next, polytetrafluoroethylene powder was added to 0.2 g of this composite as a binder and mixed, and the obtained electrode mixture was pressure-molded together with a current collector made of an aluminum mesh to obtain an electrode mixture. An electrode was obtained by crimping to a current collector. The composition of the electrode mixture at this electrode was vanadium pentoxide: acetylene black: polytetrafluoroethylene = 38: 58: 4 (weight ratio). The above electrode is punched into a circle with a diameter of 15 mm to form a positive electrode, and a disc-shaped lithium with a diameter of 17 mm is used for the negative electrode.₄A coin-shaped lithium secondary battery having a diameter of 20 mm and a height of 1.6 mm was produced using propylene carbonate in which

[0024] Example 2 0.1 g of acetylene black, 2 g of water and 1 g of acetone were added to 3.8 g of a colloidal solution of vanadium pentoxide obtained in the same manner as in Example 1, and the mixture was mixed and dispersed by stirring with a stirrer for 3 hours. Further, dispersion treatment was performed for 5 minutes with an ultrasonic homogenizer to prepare a dispersion liquid. This dispersion was applied to an aluminum foil and heat-treated at 120 ° C. for 3 hours to obtain an electrode having a film of a composite of vanadium pentoxide and acetylene black formed on the surface of the aluminum foil. The ratio of vanadium pentoxide to acetylene black in this complex film was 1: 2 by weight. Hereinafter, a coin-shaped lithium secondary battery was produced in the same manner as in Example 1.

Comparative Example The colloidal solution of vanadium pentoxide obtained in the same manner as in Example 1 was heat-treated at 120 ° C. for 3 hours to obtain a fine powder of vanadium pentoxide. The fine powder of vanadium pentoxide and acetylene black were mixed at a weight ratio of 7:10, and the bulk density of the obtained mixed powder was measured. The bulk density of this mixed powder was 0.046 g / cm.³Met. That is, when the fine powder of vanadium pentoxide and acetylene black were mixed at the same ratio as the composition ratio of the complex of Example 1, the bulk density was as small as 1/10 or less of that of the complex of Example 1. It was inferior in filling property.

[0026] The fine powder of vanadium pentoxide is mixed with acetylene black and polytetrafluoroethylene, and the electrode combination has a composition ratio of vanadium pentoxide: acetylene black: polytetrafluoroethylene = 38: 58: 4 (weight ratio). When the agent was prepared and an attempt was made to prepare an electrode in the same manner as in Example 1, the binding property between the particles was poor and the electrode could not be prepared. Therefore, the ratio of polytetrafluoroethylene was increased, and the composition was changed to vanadium pentoxide: acetylene black: polytetrafluoroethylene = 33: 50: 17 (weight ratio) to prepare an electrode.

[0027] Hereinafter, a coin-shaped lithium secondary battery was produced in the same manner as in Example 1. Charge / discharge tests (charge cut voltage: 4.2 V, discharge cut voltage: 2.0 V) were performed on the lithium secondary batteries of Examples 1 and 2 and Comparative Examples at various current densities, and the discharge capacity was measured and output. The characteristics were evaluated. The results are shown in Fig. 3. The current density in FIG. 3 is represented by the current value per unit area of the positive electrode, and the discharge capacity is represented by the discharge capacity per unit weight of vanadium pentoxide.

As is clear from the results shown in FIG. 3, the discharge capacity of the battery of Comparative Example 1 was remarkably reduced as the current density was increased, but the batteries of Examples 1 and 2 were discharged even when the current density was increased. The capacity was hardly reduced, and in particular, the battery of Example 2 in which the electrode did not contain a binder had extremely good output characteristics.

[Brief Description of Drawings] FIG. 1 is a schematic view showing an example of the shape of the electrode material of the present invention. FIG. 2 is a schematic view showing an example of the cross-sectional shape of the electrode material of the present invention. FIG. 3 is a diagram showing the output characteristics of the lithium secondary batteries of Examples 1 and 2 and Comparative Example.